In the machining of a workpiece by means of a laser beam, for example in the cutting of the workpiece by means of a high-power laser beam, the position of the focal point of the optical focusing system relative to the workpiece surface is of great importance.
When using a conventional laser tool, in order to set or to maintain constant the spacing between the tool head or the focal point of the optical focusing system and the workpiece, a sensor electrode is fitted to the tool head, which sensor electrode measures the actual spacing between the tool head and the workpiece surface, for example using capacitance. The signal obtained from the sensor electrode is passed to a regulating device which compares the measured actual spacing with a theoretical spacing and balances a corresponding difference by suitable drive of a drive motor connected to the tool head. In this way, a desired spacing between tool head and workpiece surface can be maintained independently of the course of the workpiece surface. This also means that during the machining of the workpiece the spacing between the focal point of the optical focusing system and the workpiece surface no longer changes.
However, the aforementioned drive motor must move the entire tool head, which, on its part, is mounted on a supporting arm. Accordingly, the laser tool has relatively great inertia, since, on account of the high mass of the tool head, it cannot react very rapidly to changes of spacing between tool head and workpiece surface. Thus, the laser tool exhibits only a low working speed.
In the case of the conventional tool head, the optical focusing system and the lens mounting cannot be adjusted during the operation of the tool head. For this purpose, it would be necessary to act manually on the tool head; this being virtually impossible during the operation thereof. Only before the operation of the tool head can the optical focusing system be adjusted via the lens mounting in the direction of the laser beam, for which purpose a setting ring is situated at the external surface of the tool head, which setting ring appropriately displaces the lens mounting upon rotation.
EP 0,306,456 A1 discloses a further tool head in the case of which the optical focusing system for the laser beam is disposed within a nozzle. However, the optical focusing system and the nozzle are fixedly connected to one another. Accordingly, in order to regulate the spacing between tool head and workpiece surface by means of a sensor electrode, the nozzle, the optical focusing system and a cylindrical coil carrier with an externally applied coil are displaced in relation to a magnet, so that a laser tool exhibiting this tool head also has relatively great inertia, in consequence of the large masses which are to be displaced.